On the self-excitation mechanisms of Plasma Series Resonance oscillations in single- and multi-frequency capacitive discharges

TL;DR

This paper investigates the mechanisms behind plasma series resonance oscillations in capacitive discharges, revealing new nonlinear effects that can cause self-excitation even in symmetric configurations, expanding understanding beyond previous asymmetric-focused models.

Contribution

It identifies additional nonlinear mechanisms, such as cubic charge-voltage relations and time-dependent plasma frequency, that enable PSR oscillations in symmetric discharges, previously thought to occur mainly in asymmetric ones.

Findings

Cubic charge-voltage contributions can induce PSR oscillations.

Time-dependent plasma frequency influences resonance self-excitation.

Symmetric discharges can exhibit PSR oscillations due to these mechanisms.

Abstract

The self-excitation of plasma series resonance (PSR) oscillations is a prominent feature in the current of low pressure capacitive radio frequency (RF) discharges. This resonance leads to high frequency oscillations of the charge in the sheaths and enhances electron heating. Up to now, the phenomenon has only been observed in asymmetric discharges. There, the nonlinearity in the voltage balance, which is necessary for the self-excitation of resonance oscillations with frequencies above the applied frequencies, is caused predominantly by the quadratic contribution to the charge-voltage relation of the plasma sheaths. Using PIC/MCC simulations of single- and multi- frequency capacitive discharges and an equivalent circuit model, we demonstrate that other mechanisms such as a cubic contribution to the charge-voltage relation of the plasma sheaths and the time dependent bulk electron plasma frequency can cause the self-excitation of PSR oscillations, as well. These mechanisms have been neglected in previous models, but are important for the theoretical description of the current in symmetric or weakly asymmetric discharges.